MD Anderson Media

Chapter 1: Introduction to Prenatal Diagnosis

  • Overview of Prenatal Diagnosis

    • Involves screening and diagnostic tests to identify abnormalities.

    • Screening Tests: Identify higher risk individuals but do not provide a diagnosis.

    • Diagnostic Tests: Confirm diagnosis of abnormalities if present.

  • Evolution of Recommendations

    • Historically focused on women of advanced maternal age (AMA).

    • ACOG now recommends prenatal diagnosis for all pregnant women, offering various tests regardless of age.

  • Common Diagnostic Tests

    • Used to detect chromosomal and phenotypic abnormalities.

    • Not all chromosomal abnormalities are detectable via standard cytogenetic analysis.

    • Microarray Analysis: Useful for identifying smaller deletions/duplications that chromosomal analysis might miss.

  • Uni parental Disomy (UPD)

    • Refers to inheritance of both chromosomes from one parent for a given homologous pair.

  • Limitations in Diagnostic Testing

    • Cytogenetic analysis might miss low-level mosaicism—abnormal cell lines not represented in an amniotic sample.

    • Single gene disorders can be diagnosed if there is evidence of parental carrier status.

  • Testing Samples in Prenatal Diagnosis

    • Amniotic Fluid: Commonly used for chromosome analysis.

    • Chorionic Villi Sampling (CVS): Involves testing placenta samples; limited to placental cells.

    • Fetal Blood Sampling: Rarely performed, typically when detailed confirmation is needed.

    • Samples from cystic hygromas or fetal urine can also be used for analysis under specific conditions.

  • Procedural Considerations

    • Risks of invasive procedures must be communicated to patients.

    • Decisions often made based on previous pregnancy histories or abnormal screening results.

Chapter 2: FISH or Trisomy Tests

  • FISH (Fluorescence in situ Hybridization) Testing

    • Quick test to detect aneuploidy of chromosomes, commonly used in prenatal settings.

    • Results can be returned rapidly, usually within the same day.

    • Complementary to confirmatory cytogenetics; not standalone.

  • Limitations of FISH Testing

    • Not all chromosomal abnormalities are covered by the panel; potential for false-negative results.

    • Technical artifacts could affect results, especially in poorly collected samples.

    • Every positive test should be confirmed with further chromosome analysis.

  • Examples of Clinical Cases

    • Case studies where false positives/negatives in FISH testing highlighted the importance of confirmatory tests.

Chapter 3: Understanding Chromosomes

  • Karyotyping and Chromosomal Analysis

    • Essential for visualizing chromosomes and detecting abnormalities.

    • Cases demonstrate how translocations can complicate interpretations of results.

  • Recurrence Risks

    • Varies by genetic abnormalities; translocations significantly raise risk rates compared to trisomies.

Chapter 4: Mosaicism and Analysis

  • Definition of Mosaicism

    • Presence of two or more genetically different cell lines in one individual.

    • More common in prenatal samples derived from placental tissues versus fetal tissues.

  • Reporting Standards

    • Level one mosaicism: rarely reported.

    • Level two mosaicism: moderate workup required.

    • Level three mosaicism: always reported due to significant implications.

Chapter 5: Addressing Abnormal Results

  • Handling Inconclusive Findings

    • Assessing cases with conflicting results to determine clinical significance.

    • Follow-ups often include parental karyotyping for accurate risk assessments.

  • Clinical Implications for Parents

    • Counseling is crucial; outcomes can influence important decisions.

Chapter 6: Parental Considerations in Genetic Testing

  • Uni parental Disomy (UPD)

    • Can have significant clinical consequences, including unmasking of recessive genes.

  • Clinical Examples of UPD Cases

    • Instances where UPD played a role in genetic conditions observed in offspring.

Chapter 7: Normal and Abnormal Cell Analysis

  • Diagnostic Challenges

    • Examples of abnormal findings from karyotype results leading to potential mix-ups.

    • Importance of additional tests (e.g., SRY FISH) to clarify gender anomalies.

Chapter 8: Conclusion

  • Summary of Prenatal Diagnostics

    • Highlights the complexity and psychological weight of prenatal testing.

    • Genetic counseling connects clinical findings with patient decisions.